Observation of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mfrac><mml:mrow><mml:mi>J</mml:mi></mml:mrow><mml:mrow><mml:mi>ψ</mml:mi></mml:mrow></mml:mfrac><mml:mn/><mml:mo>(</mml:mo><mml:mn>3100</mml:mn><mml:mo>)</mml:mo><mml:mn/></mml:math>Production by 209-GeV Muons

Interactions of 209-GeV muons within a magnetized-steel calorimeter have produced 1000\ifmmode\pm\else\textpm\fi{}80 ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ pairs from $\frac{J}{\ensuremath{\psi}}(3100)$ decay. Redundant systems of proportional and drift chambers maintained uniform acceptance and 9% mass resolution. Above 30 GeV, the cross section for $\ensuremath{\psi}$ production by virtual photons is found to rise less steeply with energy than predicted by a quantum chromodynamics calculation. Its dependence on ${Q}^{2}$ fits the vector-dominance form ${(1+\frac{{Q}^{2}}{{M}^{2}})}^{\ensuremath{-}2}$ with $M=2.7\ifmmode\pm\else\textpm\fi{}0.5$ GeV.